1. Field of the Invention
The present invention relates to an inkjet head used in an inkjet recording apparatus for ejecting ink onto a recording medium to perform printing.
2. Description of the Related Art
In an inkjet head, ink from an ink tank is supplied to a plurality of pressure chambers through common ink paths. When pulse-like pressure is selectively given to the pressure chambers to generate pressure wave, ink is ejected from nozzles connected to the selected pressure chambers. Of this type inkjet heads, an inkjet head having pressure chambers arranged in the form of a matrix along a head surface has been proposed to achieve higher print resolution and higher print speed (e.g., see Japanese Patent No. 3,231,786 (FIGS. 3 and 4), U.S. Pat. No. 5,757,400 and WO 97/28000).
In the proposed inkjet head, hexagonal pressure chambers are arranged in one direction along a head surface to thereby form pressure chamber columns. Common ink paths for supplying ink to the pressure chambers extend in the direction of arrangement of the pressure chambers. Opposite sides of pressure chambers constituting each pressure chamber column are partially opposite to two common ink paths respectively when viewed from a direction perpendicular to the head surface. Nozzles are arranged in central portions of the pressure chambers respectively when viewed from the direction perpendicular to the head surface. Ink is supplied from common ink paths on opposite sides of the pressure chambers into the pressure chambers. The ink is ejected from the nozzles located in the central portions of the pressure chambers.
In the inkjet head described in Japanese Patent No. 3,231,786, the distance between nozzles in two adjacent pressure chamber columns is however made large because the nozzles are arranged in central portions of the pressure chambers respectively. The nozzles for ejecting ink need to be arranged in positions not overlapping the common ink paths when viewed from the direction perpendicular to the head surface. If the nozzles are arranged in this manner, the width of common ink paths disposed on opposite sides of each pressure chamber column is limited. If the width of common ink paths is limited in this manner, the flow path area of the common ink paths is inevitably narrowed. For this reason,the flow path resistance of the common ink paths increases, so that ink cannot be smoothly supplied to the pressure chambers. Or the height of each common ink path must be made large in order to increase the flow path area of the common ink paths. As a result, the size of the head increases.